The present invention relates to a video signal output apparatus suitable for use in a video disk player.
FIG. 1 is a block diagram showing a conventional video signal output apparatus used in a video disk player. Reference numeral 1 designates a video signal generator circuit constituted by, for example, a video signal processor, a frame memory, or the like, and arranged to generate a video signal, and 2 designates a video signal generator circuit constituted by, for example, a disk reproducing circuit or the like, and arranged to generate a video signal similar to the circuit 1. The generator circuit 2 supplies a control signal (an inhibit signal) to a control circuit 5, for example, before a CAV disk is started, or before a predetermined frame is searched in scanning a CLV disk. The control circuit 5 changes over a switch 3 to connect it to the generator circuit 1 before the generator circuit 2 is enabled to produce a video signal, so that the video signal produced by the generator circuit 1 is displayed through the switch 3 by a display 4 constituted by a television image receiver or the like.
The generator circuit 2 reverses the control signal (to produce an enable signal) when the generator circuit 2 is enabled to produce a video signal. At that time, the control circuit 5 changes over the switch 3 to connect it to the generator circuit 2. As a result, in place of the video signal produced by the generator circuit 1, the video signal produced by the generator circuit 2 is selected and displayed by the display 4 through the switch 3.
Thus, the video signal from the generator circuit 1 is displayed before the generator circuit 2 is enabled to produce a video signal so as to prevent the display 4 from being in a nondisplaying state.
As described above, the conventional apparatus is arranged such that, as soon as the generator circuit 2 is enabled to produce a video signal, the video signal from the generator circuit 2 is immediately outputted in place of the video signal from the generator circuit 1. However, there is a disadvantage in that the vertical synchronizing signal of the video signal of the generator circuit 2 is not always in phase with the vertical synchronizing signal of the video signal of the generator circuit 1 and the displayed picture is disturbed by the phase difference between the respective vertical synchronizing signals at the point of time when changeover is performed.
It is therefore an object of the present invention to prevent a displayed picture from being disturbed at the time of changeover.